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Steady-Floating Marine

Structures

By Waldon Fawcett

HERE has recently been patented in the chief military, naval, and commercial countries of the world an invention which is likely to modify in many different ways the construction of breakwaters, wharves, jetties, etc. It will also introduce an entirely new system of providing stable floating foundations in wave-disturbed waters, for defensive forts, coaling stations, lighthouses, and similar marine structures.

The scientific principle that forms the basis of the patents is an extremely simple one; but the practical working-out of the engineering details has required several years of patient investigation and experiment on the part of the inventor, William E. Murray, a resident of Los Angeles, California.

It will come as a new thought to many people-although a moment's reflection

will make its truth obvious that when the ocean surface is broken with waves, and even when it is lashed by the wind into heaving and tumultuous billows, the disturbance is only a surface one. In point of fact, the wave-disturbance extends to a depth seldom exceeding fifteen feet. Below this level there is absolute stability; and where there are no currents, the ponderous mass of water, growing denser and denser with increasing depth, rests on the ocean bed firm and immovable.

It was by taking advantage of these static conditions at a depth beneath the surface of the sea, that the Murray system of stable flotation was devised. Ships float almost entirely in the wavedisturbed stratum of the waters, only the lower part of the hull of those of considerable draught being in the steady waters deeper down. Consequently their equilibrium is not maintained; there is

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no effective resistance to the thrusts and blows of the billows, and vessels accordingly pitch and roll under the influence. of the heaving waves. A ship built according to the rules of scientific shipbuilding cannot turn turtle; however far she may heel to one side or the other, she will always right herself. But no method of ship-construction has yet been devised that makes the vessel steady in tumbling waters. The biggest, heaviest,

deep-sea floating lighthouse-then it makes possible what hitherto has been deemed impossible. The fortress may have its gun platform, rising out of the tossing waters, so steady that a tumbler full of water will not spill; and the lighthouse, with its guiding beacon two hundred feet above the wave-disturbed surface of the ocean, will stand straight and firm, just as steady as if it were built on solid rock foundations.

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STEADY-FLOATING BREAKWATER.

and deepest-draught liner afloat has most of her immersed bulk in the disturbed surface water, and is therefore, although in somewhat less degree than smaller craft, still sensitive to wave action. The same with men-of-war. The steady flotation of battleships, although long recognized as a desideratum of first importance, has been found impossible of attainment, so that the aim of their guns, except when the sea is quite calm, can never be from a stable platform, and in really tempestuous weather must always be more or less unreliable.

The Murray invention has nothing to do with ordinary sea-going craft, which are built primarily for speed and for cargo-carrying; but where these factors do not count-where, for example, a steady-floating fortress is required, or a

How are these apparently abnormal results obtained? Simply by immersing the floating structures in the fardown stable waters to such a depth, in such a way that the action of the heaving surface waters cannot cause oscillation. On a floating body built according to this plan, the thump of a big billow such as would make a great ocean liner careen, has no unsteadying effect.

To begin with the simplest form of these steady-floating structures, let us take a hollow upright cylinder of iron, having attached to its lower end a broad projecting flange, weighted with pigiron, stones, or other heavy material. Such a body will float vertically in the water with the projecting flange for a base. The latter, if the length of the cylinder be sufficient, will be immersed at such a depth in the dense, stable waters as to be virtually embedded in a resisting medium. Anyone having a knowledge of the scientific principle of the lever, will at once understand that the action of the waves on the superstructure is negatived by the resistance of the deeply submerged portion of the floating.

body-that any blow above is counteracted by the strong leverage below, checking any tendency to oscillation.

The greater the depth of submersion, the greater the resistance; for, with increased depth, there is increased density of the water, so that the substructure suspended in this medium becomes more and more immobile. But the broad and sufficiently deep projecting flange plays the all-important part of rendering submersion to any inconvenient depth unnecessary, thus making the device of practical utility in comparatively shallow waters. The flange and the lower portion of the cylinder together displace a sufficient volume of the steady water beneath the region of wave disturbance to maintain the whole body in stable equilibrium, unaffected by the motion of the waves playing around the upper part of the cylinder. It is this combination of the wide-projecting flange with the comparatively short cylindrical tube, which affords the key to the solution of the entire problem of steady flotation for marine structures of a great variety of forms and for a wide diversity of uses.

Let us illustrate the application of the principle to a floating fortress. Deep down below the wave-disturbed waters is the hollow, projecting flange properly weighted, which affords for the gun platform above the surface of the sea a wide

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STEADY-FLOATING LIGHTHOUSE.

STEADY-FLOATING FORT.

and immobile foundation- a "floating foundation," it may be termed, for the words, under these conditions, cease to be contradictory. With water ballast used as part of the weighting material, the platform may be sunk close to the surface of the sea; or, by pumping out some of the water, it may be raised to any required elevation. This, then, forms the patented Murray steady-floating fortress with annular revolving deck; and an examination of its special features will show that a remarkable new machine for both defensive and offensive purposes has

been evolved.

It is conceded that shore batteries are now inefficient for the defense of cities and harbors against attack by modern. battleships; but the Murray floating fortresses can be placed far enough off shore-say, three or four miles-to form a perfect screen of defense that no fleet can approach with impunity. These forts will expose only a small target surface above water; and this will not only be proof against the most modern guns, but the sloping face will cause any striking shells to glance off with comparative harmlessness. Within will be mounted the biggest guns, and the annular revolving platform will give these every direction and great rapidity of fire.

For naval and military purposes, the principle of steady-floating structures can be developed in many other ways. For example, torpedo stations can be placed still further out to sea than the floating fortresses, forming an additional

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WILLIAM E. MURRAY, OF LOS ANGELES, CAL. An engineer who has invented and patented a system of steady-floating structures.

deadly barrier to an attacking fleet. These would not only be unseen by the enemy, but would afford a steady platform from which to discharge the torpedoes. All would be connected with one another and the shore by telephone or telegraph.

But the invention is just as important for commercial uses as for coast-defense purposes. By way of example, let us take the Murray steady-floating wharf. There is hardly a harbor or sheltered sound along our coast where there are not water frontages that cannot be turned to use for wharfage purposes, the water being too deep for piling to be driven, and the expense of filling in with rock being prohibitive. Here steady floating wharves can be run out, at which ships can discharge or load their cargoes directly into or out of the railroad

cars. As the wharves rise and fall rigidly with the tides, the ship is always at the same level with the landing stage, which greatly facilitates the handling of cargo.

Similarly, on what has hitherto been an exposed and shelterless coast, a complete sheltered roadstead may be constructed, by means of a floating breakwater out at sea, affording a harbor of refuge, and also protecting the floating wharves and jetties of a commercial seaport. This system will make it possible for railway companies to provide themselves with terminal facilities at any point along a coast, and at a fraction of the cost at which it is now possible to construct harbor works in exposed positions.

Another illustrative example is the steady-floating lighthouse. These can be placed in the deepest and roughest waters, where hitherto it has been impossible to construct such works, owing to the difficulties in obtaining foundations. They can be placed at any distance off shore, thus adding greatly to their efficiency, as shipping can be directed in a course much farther away from a dangerous coast.

The invention is also applicable for railroad bridges across deep water, for coaling stations out at sea along the routes of mercantile shipping, and for floating wrecking platforms wherewith to raise sunken vessels. Floating hotels and sanitariums, hospitals, bath houses, and telegraph stations may also be mentioned, just to indicate the wide range of utility possessed by these structures, designed to be steadily floated in deep waters, close in shore or far out to sea, and all immovable and unaffected by the action of the waves and winds. Their steadiness makes secure anchoring easy; for, in the case of a ship, it is the plunging and jerking that causes the real strain on the hawsers.

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Largest Concrete Bridge

W

By Guy E. Mitchell

Secretary, National Irrigation Association

ITH the increased use of concrete as a building material, it is not at all strange that bridge engineers are turning to this most stable and yet flexible product with which to construct spans for travel across rivers To show the confidence these engineers have in concrete, one need but look upon the new Connecticut Avenue bridge now nearing completion at Washington, D. C., which is believed to be the largest concrete bridge in the world.

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and ravines.

What is now understood to be the largest concrete bridge standing in this country, is the "Big Muddy" bridge on the Illinois Central Railroad. This structure, however, is only one-fifth the size of the Connecticut Avenue bridge; it was built in 1902, and consists of three 140-foot arches, requiring 12,100 cubic yards of concrete.

Compared with the other bridges in this country and in Europe, the bridge at Washington stands in a class alone. Nowhere else has an attempt been made to build so great a number of arches of such great size as in the present case, entirely of concrete, without steel framing to support the mass. Each of the five principal arches is 150 feet in length; and the bridge at its highest point will be 150 feet above the bottom of Rock Creek gorge, which it crosses. The total length of the structure between the abutments, is 1,341 feet, or 21 feet more than a quarter of a mile.

In addition to the five main arches, there will be four smaller

ones, two at each end, making up the abutment piers. The total amount of masonry in the nine arches is nearly 13,000 cubic yards. The foundations for the piers of this bridge were carried down to depths varying between 20 and 40 feet, to solid rock, where it could be reached economically, and in other cases to hard, rotten rock. It is estimated that the total weight of this structure from its foundation will be about 16 tons per square foot. In constructing the huge arches, a great amount of lumber was employed in erecting the "centering." In this work one and a-half million board feet of Georgia pine lumber was used, this item alone costing in

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